Tag Archives: atom

Feedback loop

A cesium atom oscillates 9,192,631,770 times every second. That never changes.

What does change is the atoms’ energy state. The excited cesium atoms bounce off the detector every time the microwaves hit the same frequency as the atoms’ oscillations. The detector sends a signal to the microwave resonator, so that the microwave frequency is adjusted to sync better with the atoms. This is called a feedback loop. The detector sends a signal, the signal adjusts the microwave frequency, the microwaves excite the atoms, the atoms bounce off the detector, the detector sends a signal, the signal adjusts the microwave frequency, the microwaves excite the atoms…over and over and over. The time between each signal is exactly one second. No gears, no moving parts to oil, nothing mechanical.

That’s it! That’s how the atomic clock works. Thanks for sticking with me for an entire week on this. Finally, we can get on with our lives!

As with my explanation of the liquid crystal display, this is a simplification. I left out a lot of stuff. It’s the idea, the principle, that I was interested in explaining. Luckily for you, here are links to click on if you’d like more exact, in-depth info about atomic clocks.

https://www.livescience.com/32660-how-does-an-atomic-clock-work.html
https://www.timeanddate.com/time/how-do-atomic-clocks-work.html
https://www.gps.gov/applications/timing/


https://science.howstuffworks.com/question40.htm
https://www.fda.gov/radiation-emitting-products/resources-you-radiation-emitting-products/microwave-oven-radiation
https://science.howstuffworks.com/atomic-clock3.htm
https://www.britannica.com/technology/atomic-clock

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Radio waves

It’s late at night. Maybe you’re staying in a cabin out in the woods. You’re awake. No cell service, no tv, no computer. Only an old battery-powered radio—the kind that has a dial to tune in stations. How about listening to some music? You turn on the radio, get a lot of static, play with the dial until— “Hey! there’s a song I really like!” —but it’s faint, you lose the signal, you slo-o-o-o-owly turn the dial back and forth…there it is! You love this song! It resonates! You start humming along with the music.

Radio waves are electromagnetic energy sent from a broadcasting antenna. The energy is literally sent out in a wavy line. The number of waves sent out per second (their frequency) is expressed in a unit called hertz (Hz). One thousand hertz is a kilohertz (KHz), 1 million hertz is a megahertz (MHz), and 1 billion hertz is a gigahertz (GHz). Hertz is the number you see on a radio’s band.

When you get up between 1 billion and 3 billion hertz (1 GHz – 3Ghz) we’re talking about microwaves.

Microwaves agitate the water molecules in a cold slice of pizza to heat it up.

Inside an atomic clock, a broadcast antenna sends out microwaves inside the vacuum tube where the cesium atoms hang out. The frequency increases and decreases slightly (like tuning in a radio station) until it hits the exact same frequency as the atoms’ oscillations (9,192,631,770 times every second). The atoms resonate with the microwaves and change into a different energy state. They’re in such a fantastic mood they bounce off a detector at the other end of the tube.

https://www.youtube.com/watch?v=sRX2EY5Ubto start at 2:45
https://www.explainthatstuff.com/antennas.html
https://www.nasa.gov/directorates/heo/scan/communications/outreach/funfacts/txt_radio_spectrum.html
https://www.livescience.com/50259-microwaves.html
https://www.britannica.com/video/214986/How-radio-works-overview-radio-waves-frequency-amplitude-modulation

I’m glad the atoms are happy but I still don’t get out how this translates into keeping time. Please continue to hold.

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Cæsium steam

Cesium, like every element, is made up of only one kind of atom. There are only cesium atoms in cesium.

I just had this information tattooed on my forehead in mirror writing, so I don’t forget.

Here’s how you get cesium atoms to float around: you boil the cesium. Cesium melts at room temperature, like an ice cube melts into water. So all you need to do to get cesium atoms is boil cesium until it turns into cesium steam. Then you funnel the cesium steam down a tube which is a vacuum—nothing else in there, no air, just cesium atoms and that’s it. Then you expose those atoms to radio waves. When the radio waves hit the exact same frequency as the atoms’ own oscillations—9,192,631,770 times per second—the atoms change to a different energy state.

https://science.howstuffworks.com/atomic-clock3.htm
https://education.jlab.org/qa/atom_02.html

I guess I need to research radio waves now. Great merciful Zeus, I’m never getting to the end of this. Thanks for holding while I go look up radio waves.

 

Wow—that hold music is awful. Back to the beginning of The Western Civ User’s Guide to Time & Space

 

Please continue to hold while I sort this thing out

Remember how mechanical clocks are prone to lose time? It’s because they’re made out of physical machinery—pendulums or mainsprings and gears. We replaced those mechanical parts with a quartz crystal, zapped it with electricity to make it vibrate and got digital clocks. Digital clocks are more reliable, but they still lose 15 seconds every month.

To make the even-more-reliable atomic clock, we replaced the quartz crystal with atoms. Atoms vibrate on their own. We’re building a clock that’s as free of physical, mechanical parts as we can manage in this bad old fallen world.

Here’s what I’m getting from my exhaustive research so far: somehow cesium atoms are funneled down a tube. How do they get the atoms out of the cesium? I don’t know. The atoms are exposed to radiation—radio microwaves like the kind you use to heat up your old cold French fries—which makes them switch back and forth between energy states. The idea is to tune the radio waves to sync up with the atom’s own vibrations at 9,192,631,770 times every second. It’s not easy to get this exactly right—like tuning in a jazz station from 2 counties over on an old radio with dials. There’s a detector at the end of the tube. When the radio waves are at the exact right frequency (the same frequency as the atoms’ vibrations), the atoms change energy states and bounce off the detector—which means one second has passed. Then what? I dunno. How does the detector know when the atoms change from State B back to State A ? I dunno.

Back to my research. Thanks for your patience. Please continue to hold.

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Atomic Clocks

We’re now at the point where we can talk about…atomic clocks, which lose only one second every 100. Million. Years. Yay!

What is an atomic clock and how does it work? That’s an excellent question. Honestly, I have no idea. You would think, as an adult grown-up-type guy, I’d know something like that. I don’t. I avoided science classes in school so I could hang out in the art room.

I don’t know how you get atoms to float around in a tube so you can zap ‘em with radio waves until they change into a different energy state and bounce off a detector that counts the atoms in their new changed state and funnels the whole mess into a feedback loop…

I need to go away for a few days and marinade myself in sciency research until I figure this one out. I’ll be back. In the meantime, please enjoy this hold music—

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